When the decision came to play, Rivera talked to his team about Jovan Belcher, the Chiefs linebacker who had killed his girlfriend and then turned the gun on himself. Then he tried to get his players to regain their focus in the hours before kickoff.
They never quite managed to do it.
Cam Newton threw for 232 yards and three touchdowns, and DeAngelo Williams ran for 67 yards in place of the injured Jonathan Stewart, but the Chiefs banded together to forge a 27-21 victory that snapped their own eight-game losing streak that suddenly seems trivial.
After the game, Rivera met Chiefs coach Romeo Crennel at midfield and gave him a hug.
"They played an inspired game," Rivera said. "They did some really good things, and we have to give them credit. They suffered through a difficult time and rallied as a team."
Brady Quinn threw for 201 yards and two touchdowns and Jamaal Charles ran for 127 yards for the Chiefs, who were still coming to grips with the tragedy that unfolded early Saturday.
That's when Belcher shot his girlfriend multiple times at a residence near Arrowhead Stadium, then drove quickly to the team's practice facility and turned the handgun on himself as Crennel and general manager Scott Pioli looked on from the parking lot.
"As far as playing the game, I thought that was the best for us to do, because that's what we do," Crennel said, tears forming in the corner of his eyes. "We're football players and football coaches and that's what we do, we play on Sunday."
Kansas City police have not released a motive for the shootings, which claimed the life of Belcher and 22-year-old Kasandra M. Perkins, and left a 3-month-old girl, Zoey, an orphan.
Belcher's locker was left with his jersey hanging on a hook.
"In moments, tragedies like this, they can define you or redefine you," Quinn said, "and I think this team took an event and allowed it to redefine us."
Peyton Hillis had a touchdown run for Kansas City (2-10), while Tony Moeaki and Jon Baldwin had TD catches. Ryan Succop hit a pair of field goals, including a 52-yarder with 4:54 left.
The Panthers (3-9) promptly went three-and-out, and the Chiefs were able to run the clock down to 31 seconds before giving back the ball. Newton completed two quick passes to reach the Carolina 38, but his heave as time expired was caught by Steve Smith short of the end zone.
Smith, Greg Olsen and Louis Murphy caught the Panthers' three TD passes.
"I knew that this was going to be an emotional game for the Kansas City Chiefs as a whole, and I know they wanted to come out and win," Newton said. "For us to play as a team, we have to know that, know we're going into a hostile environment and we still have to produce."
Kansas City produced from the start, with Hillis powering in to score the team's first touchdown on an opening possession since Dec. 26, 2010. It was also the first TD drive engineered by Quinn since December 2009, when he helped the Browns beat the Chiefs at Arrowhead Stadium.
Hillis ran to the sideline after scoring his first touchdown of the season and handed the ball to Crennel, then gave the affable head coach a big bear hug.
The Panthers answered with their own long touchdown drive, which was capped by a 47-yard touchdown pass to Olsen. And after the Chief stacked on a field goal, Carolina scored again when Newton hit Smith in the corner of the end zone for a 14-10 lead.
But Kansas City finished off the half with one of its best drives of the year, an 80-yard march that took up the final 7:25. Hillis was stuffed at the line on third-and-goal, and Crennel allowed the clock to hit 2 seconds before calling timeout. On the final play of the half, Quinn saw Moeaki open in the back of the end zone and delivered a soft toss for a 17-14 lead.
Breathing room came late in the third quarter when the Chiefs used 17 plays to go 87 yards on a drive that lasted another 10 minutes. Quinn finished it with a 3-yard touchdown pass to Baldwin.
Carolina mounted a comeback with the opening drive of the fourth quarter, with Newton hitting Murphy on a quick slant route from the 8 to get the Panther within a field goal.
The Chiefs added their own field goal, and then labored through the final minutes before pouring on the field, hugging each other and then kneeling in prayer around the midfield logo along with several members of the Panthers.
"There are lots of games that have a side story," Carolina offensive lineman Jordan Gross said. "We're football players, and we've been playing for a long time. We know when the ball is on the field, we're lined up to play, to forget about it. But it's a lot easier for us than them."
NOTES: Chiefs CB Brandon Flowers (hamstring), S Abe Elam (left leg) and LB Derrick Johnson (left hamstring) left the game with injuries. Carolina lost LB James Anderson (eye), Murphy (foot) and S Sherrod Martin (right knee) during the game. ... Chiefs WR Dwayne Bowe caught four passes to move into third place in franchise history with 413 catches. ... Carolina still has only attempted 11 FGs this season.